Manufacture of cellulosic articles



June 27, 1950 G. RAY, JR 2,512,963

MANUFACTURE OF CELLULOSIC ARTICLES Filed April 10, 1946 2 Sheets-Sheet 1IN V EN TOR.

m'ow c. RAY JR. BY

ATTORNEY June 27, 1950 G. RAY, JR 2,512,968

MANUFACTURE OF CELLULOSIC ARTICLES Filed April 10, 1946 2 Sheets-Sheet 2FIGB.

FIGZ.

ION MOLALITY FIG.4.

INVENTOR.

NT ON G. RAY JR.

BY ZZXQ/ ATTORNEY ?atentecl June 27 1950 MANUFACTURE OF CELLULOSICARTICLES Linton G. Ray, Jr., Buflalo, N. Y., assignor to E. I. du Pontde Nemours 85 Company, Wilmington, Del., a corporation of DelawareApplication April 10, 1946, Serial No esosss (01. 18-54) I 22 Claims.

cellulose by anappropriate treatment. The product is purified and dried,preferably while it is free from substantial tension. Though rayon yarnproduced by this'rpro'cess is characterized by a high tensile strengthand relatively low elongations, it has transverse properties whichrestrict the field of its utility.

An object of this invention is to provide a new and improved method forthe manufacture of regenerated cellulose articles.

Another object of this invention is to. provide a new and improvedmethod for the production of rayon having improved physicalcharacteristics.

An additional object of this invention is to provide a method ofproducing high tenacity rayon having improved transverse properties.

Other and additional objects ofthe invention will become apparenthereinafter.

The objects of the invention are accomplished, in general, by extrudingviscose into a bath of such composition and maintained under suchconditions as to precipitate the cellulose xanthate' rapidly withoutsubstantially converting it to regenerated cellulose, stretching theunregenerated structure to a very. marked degree, relaxing theunregenerated cellulose structure in the presence of a swellingsolution, and then converting the cellulose xanthate to regeneratedcellulose by the use of any appropriate treatment.

The regenerated cellulose productis then purified and subjected, to theaction of a drying medium while it is preferably free from substantialtension.

Optionally, the relaxing treatment can be performed simultaneously withregeneration. The swelling bath in, which the gel unregenerated(cellulose xanthate) structure is relaxed includes water as the swellingagent. Since water alone is too good a swelling agent (the cellulosexanthate of the gel unregenerated yarn under no tension will dissolve inthe water), it is necessary to include a cellulose xanthate coagulant(salt) in the water, The quantityv of the coagulant is such as tocontrol and limit the swelling .when taken in connection with of theyarn in'the relaxed state. As will hereafter appear, the pH and the ionmolality'of the swelling bath must be correlated to produce the desiredresults.

' The invention may be more readily understood by referenceto thefollowing detailed description the accompanying drawings, in which:

Figure l is a diagrammatic side elevational view, with parts shown inse'ction,'of one form of an apparatus suitable for carrying out theinvention;

Figure 2 is a diagrammatic side elevational view of a detail of amodified form of apparatus for relaxing the unregenerated gel'yarns;

Figure 3 is a"diagrammatic side elevational viewof a'detail of stillanother modified form of apparatus for relaxing the unregenerated gelyarnsya'nd Figure 4 is a graph showing the pH and ion molality range ofsolutions useful for swelling gel unregenerated'cellulose structures.

For convenience, the invention will be described with particularreference to rayon, although in its broader aspects it is applicable tothe manufacture of articles having a physical shape or form differentfrom rayon.

v Referring now to the drawings wherein like reference numeralsdesignate like parts, the reference. numeral I0 designates a candlefilter to which a viscose filament-forming composition is fed in theknown manner. The] viscose-forming solution is forced through the candlefilter'lfl into and through a gooseneck [2 which is provided on thelower end thereof with a spinneret M positioned below: the surface ofthe spinning bath in a tank 16. The filaments I8 issue from thespinneret l4 below-the surface of the spinning bath in a tank I6 and arepassed about a positively driven'feed wheel 20 and cooperating freelyrotatable guide roller 22, then about freely rotating rollers 24 and 26positioned in a stretching bath in tank 28, and then about a secondpositively driven feed wheel 30 and cooperating freely-rotatableguideroller 32. The filaments are passed about the two feed wheels 20 and 30with a sufficient number of turnsto-prevent slippage of the filamentsthereon so that the peripheral speeds of the respective rollers and thelinear speedof the filaments thereon are the same. Feed wheel 30 isrotated at a higher speed than feed wheel 20'so as to impart a stretchto the filaments passing through the bath-in tank 28. The guide roller32 ispartially .submerged in a swelling bath contained in a tank 34. y

From the feed wheel 30, the yarmwet with T6 3 laxing solution, drops ofits own weight onto an eccentrically revolving plate 36 to build up ayarn cake 38. The eccentrically revolving plate is of the type describedin United States patent to Dannenberg et al. No. 2,089,159.

Instead of applying the swelling bath to the yarn by the guide roller32, as showninFigure 1,

a nozzle" 40*can be positioned relative to the feed wheel 30 so that aswelling bath solution fed 4 whereby the peripheral speed of the rollerand the linear speed of the filaments were the same. Due to the speedsimparted to the filaments on the first and second positively drivenrollers, the

-; filaments were stretched during their passage through the second bathapproximately three times-their original 1ength;'i. entheirlength at thefirst driven-roller'tthe stretch-thus being approximately 200%). Thissecond bath was thereto will be' supplied to the unregenerated' l-iomaintained at 100 C.

fcellulose filaments on such feed wheel.

"scribed embodiments for subjecting thege'lun regenerated filament tothe' 'sw'elli'ng bath, the

The filaments'after stretching were then subjdtdto a'relaxiiig bath,positioned as shown in Figure l"ofthevdrawings, prepared from 12%sodiumasu lfate and 88% water. Such bath, which filaments, after leavingthe feed"wheel -?ilI,"-c'an* llfhad a--pH offl and an ion molality of2.9, was

be caused to pass about a positivelydrivenfeed wheel 42 and cooperatingfreely rotatable guide roller 44, then about freely rotatable rollersdfi and 48 positioned in a tank 50 containing'the swelling solution,and'then about the feedwheel 52; and-cooperating freely rotatable g-uideroller 54 "The fiiaments "can be passed about the feed rollers 42 and'52 with a sufficientanumber of turns 't'o. prevent slippage thereon.The rollers 425: aridt-52Zare rotated! at such speeds thatmo substantial: tension is --imposed =on the filamen'ts.

Thus, rollers 42 and 52 can be rQtatedFat-thesame 'speedsrblit, in thepreferred form, the? peripheral spee.d=' of roller 52, :eis. :less thanthe :peripheral speed of -roller-4 2-to)permitiyarn relaxation in the 3solution in tank 50.

In this embodiment,-the filaments; after leaving-the feed wheeliL-arecollected? into a cake in the samemanner as 1 previously described.

The following; examples illustrate certain specific embodiments of:the.= invention; it being understood that the invention is=notrestricted thereto. In the examples, the parts andproportionsxarefby weight unless otherwise specified,

and thei salt index is determined by the: method of Reinthaler-Rowe.Arti-ficial Silk (1928)., page I Viscose containing 7% cellulose, 9%so'dium hydroxide and 3 3% "carbon disulfide airid having a common salt(sodium'ohlo'ride)--index-oi 4.3 -w'as extruded througha' spmneret intoa bath prepared flbfll 20% --m6noo'( i-i1im phosphate, 16%

sodium senate mid -10% "water, to--which was t'risb'di'um soph'osphategor both, to yiel'da pI-I-'of-4.1." Thebath l was maintain'edat a te'r r'ipera-tureof app'roxiadded -sumcie'nt -phosphoric acid,

mately 55-C. i The filaments werepassed'through the bathfor a distanceof 6" without pontact with guidesorany other 'de-vi'ce which mi ghtim-55 part t'ension 'a'nd were then withdrawn froin the bath and passedfthroughai'r -a t'- normal room condition (75F5andatmospheric-pressurefor a' distan'ee ot-l2 to a positivelydrivenglass rollenbr feed wheel which impar'ted -to the filaments 0ndbalth,'fprepared from 18% monosodiumphos phate, 2% sodium'sulfate -and'80% 'water, with the 'addi-tio'n 'of -fsu'fiicient phosphoric 'acid or1 triso'diumpnospnate, 01" both; to yield a 0f4'i2,

after which the {filaments were passed around a secdntlpos'itivelydriven glass roller which"imments, The filaments 'were-passedone or moretimes-about such'iglass rollerto" preventslippage, "1s

"The- "filaments 65 Were' DasSed for a distance of'45 through asecmaintained; at room temperature F. and at mospheric pressure). Theyarn, upon leaving the'second positively driven roller and while wetwith the relaxing solution, was allowed to fall of il'iSQOW II "weightontooa fiat plate; which was so moved as 'to traverse the yarn Paccording any desired pattern-and thus-buildup a suitable cake orpackage. Thefilamentsorcyarmat this point were stil-l in the1--form:-ofcellulose xanthate tree fr-om any substantial degree of regeneration.--The cake was then covered with a cloth wrapping and immersedrfor aperiod -Of 16h0l1rS-in-a, solution at 55: C.'having the-same compositionas the first or spinning 'bath to {convert the :yarn toregenerated'cellulose. 'Theca-ke wa's removed irom theregenerating-bath." After being washed freevof occludedsalts, it wastreated with r a lubricating finish and was dried. v

:-A-comparison .of-"theipropertiesof -cyarn produced' -by this.eprccedure and of yarn produced by the identicalz procedure-'exceptthat'th treat.- ment" with =the relaxing bath is omitted(designated as ControlD is set forth hereafter-in Table A.

Viscose containing5rl %"c"ellulose,"9 l' 7 'fsodiurn hydroxideand 23i5%carbon disulfid nd'hav'ing a common "saltwodium chloride) *index of 220'wasfextruded" through 1 aspinn'er'et into a bath pre ared from 2 243mon sodimn -"pnsp1 1ate, 91 sodium sulfate and 68.6% water; to which wasadded siifiicient fph'o'sph'oric acid "triso'dium "phosphate; or both;to" yield "a; pl-I n I 315. The bath was at'a temperature o'f'approx-'irn'ately 55 C The' filaments "were passed throughYthe" bath'ffor'afdis'ta'nc'e of 6" without contact with "guides or any other devicewhich fmightfimpart' tension and'werefth'en withdrawn from th'e bath andpassed" through aira't normal room conditions ('75"F; and-atmosphericpressure).""f;orta distarl'ceof 1.4 to a" positivelydri'ven glassrbilerbrre d 'wnerwhich mpa'rted totne fiimen tsa-sp'e'e cameo" per minute.The'filamerits wereassed 'aroundi'trre"glassironer one 'or' oretinies'fto fprevent' "slippage; whereby the peripheralspeed'oftherollerand'thelinar'speed of the filaments-"were approximatelthe The" filaments werepass'ed 'for' a 'distanc'ebf "4'0 through asecond bath, prepared from 18 frionosodium priospha'te, "2%? sodiumsulfatea 0% watenwitn theaddition ofsuffiei'en pnos one an for tris'od'iu'mf'phosphate of'both; "to yield a pnfof-esyafter" which the"'fila' ents' werepassed around a "se'cohdgpdsitively ass fr'oller which;imparted a speedof "'1 8'6"i per iriinute to the filaments,The'f'fil'ameiits .we're pas's'edone frfino're "times about f-s'ubhfglass" i 'oller' to prevent slippage'flwheif y e '7 .iphemrspeea;f therollerandthe in spa d wereTanr roximatl thesame. Dueto the spe'eds"imparted tp''tii'g filaments on the first and second positively drivenrollers, the filaments were stretched during-their passage through thesecond'bath approximately 3.75 times their original length, i. e. theirlength at the first driven roller (the stretch thus being approximately275%). This second bath was maintained at 100 C.

The filaments after stretching were then subjected to a relaxing bath,positioned as shown in Figure 1 of the drawings, prepared from 11%sodium sulfate and 89% water. Such bath, which had a pH of 7 and an ionmolality of 2.6, was maintained at room temperature (75 F. andatmospheric pressure). The yarn, upon leaving the second positivelydriven roller and while Wet with the relaxing solution, was allowedto'fall of its own weight onto a fiat plate which was so moved as totraverse the yarn according to any desired pattern and thus build up a,suitable cake or package. The filaments or yarn .at this point werestill in the form of cellulose xanthate free from any substantial degreeof regeneration. The,

cake was then covered with cloth wrapping and immersed for period of 30minutes in a boiling solution, having the same composition as the firstor spinning bath but adjusted to a ,pH of 5, to convert the yarn toregenerated cellulose. The cake was removed from the regenerating bath.After being washed free of. occludedsalts, it was treated with alubricating finish andwas dried.

A comparison of the properties of yarn produced by this procedure and ofyarnproduced by the identical procedure except that the treatment withthe relaxing bath is'omitted (designated as Control) is set forhereinafter in Table A.

EXAIVIPLE III Viscose containing 7% cellulose, 9.1% sodium hydroxide and33% carbon disulfide and having a common salt (sodium chloride) index of4.5 was extruded through a, spinneret into a bath prepared frommonosodium phosphate, 10% sodium sulfate and 70% water, to which wasadded sufficient phosphoric acid, trisodium phosphate, or both, to yielda pH of 4.0. The bath was maintained at a temperatureof approximately 55C. The filaments were passed through the bath for a distance of 6"without contact with guides or any other device which might imparttension and were then withdrawn from the bath and passed through air atnormal room conditions (75 F. and atmospheric pressure) for a distanceof 14" to a positively driven glass roller or feed wheel which impartedto the filaments a speed of 450" per minute. The filaments were passedaround the glass roller one or more times to prevent slippage, wherebythe peripheral speed of the roller and the linear speed of the filamentswere approximately the same. The filaments were passed for a distance of'40" through a second bath, prepared from 18% monosodium phosphate, 2%sodium sulfate and 80% water, with the addition of sufficient phosphoricacid or trisodium phosphate, or both, to yield a pH of 3.8 to 4.2, afterwhich the filaments were passed around a second positively driven glassroller which imparted a speed of 1473 per minute to the filaments. Thefilaments were passed one or more times about such glass roller toprevent slippage, whereby the peripheral speed of the roller and thelinear speed were approximate ly the same. Due to the speeds imparted tothe filaments on the first and second positively driven rollers, thefilaments were stretched during. their passage through the second. bathvapproximately maintained at 100 0.

dried.

3.23 times their ori'ginallength, i. e. their length atthe firstdrivenroller (the stretch thus being approximately 223%) This second bath wasThe filaments afterstretching were then subthe second positively drivenroller and while wet withrelaxing solution, was allowed to fall of itsown weight ,onto' a-fiat plate which was so moved as to traverse theyarn according to any desired patternj-and thus build up a suitable cakeor package. The filaments or yarn at this point were still in the formof cellulose xanthate free from any substantial degree of regeneration.The

cake was then covered with a cloth wrapping and immersed for a period of30 minutesinya boiling solution, having the same composition as thefirst or spinning bath but adjusted to a pH of 5, to convert the yarn toregenerated cellulose. The cake was removed from the regenerating bath.After being'washed free of occluded salts, it was treated with alubricating fim'sh and was A comparison of the properties of yarnproduced by this procedure and of yarn producedby the identicalprocedure except that the treat- 1 ment with therelaxing bath is omitted(desig- -nated as Controlf) is set forth hereafter in Table A.

EXAMPLE I v Viscose containing 5% cellulose, 9% sodium hydroxide and 30%carbon disulfide and having a common salt '(sodium chloride) index of5.0

was extruded through a spinneret into a bath the bath .:for a distanceof 6" without contact with guides or any other device which might imparttension and were then withdrawn from the bath and passed through air atnormal room conditions F. and atmospheric pressure) for a distance of14" to a positively driven glass roller or feedwheelwhich imparted to'the filaments a speed'of 450" per minute. The'filamentswere passedaround the glass roller one or more timesto prevent slippage, wherebythe peripheral speed of the roller and the linear speed ofqthe filamentswere approximately the same. The filaments were passed for a distanceof. 10.7, in the air at normal room conditions (75 F. and atmosphericpressure). and thence arounda second positively driven roller which'imparted a speed of 1453" per minute. The filaments were passed one ormore times about such roller to prevent slippage whereby the peripheralspeed of theroller and the linear speed were approximately the same. Dueto the speeds im parted'to the filaments on the first and secondpositively driven rollers, the filaments were stretched in airapproximately 3.20 times their 'A comparison of the properties of theyarn produced by this procedure and of yarn produced by the identicalprocedure except that the yarn was only regenerated in the followingbath having a pH of 4.5 and an ion molality of 5.1 (designated limit ofoptimum concentration at these high pH values is limited by thesolubility of the'salt under consideration.

The graph constituting Figure 4 of the drawings shows the relationshipof the ion molality- 5 as Control). is hereinafter set forth in Table B:and pH of the solution. As shown by the curves of Figure 4, to beeffective for the invention the Per cent aqueous solution also has anion molality within Sodium sulfate 6 the-limits defined by the curves ABand CD, and Monosodium phosphate 1 preferably within the limits definedby the curves Water 79 EF and GH, and the pH at the point on theordinate of the graph corresponding to said ion Suflicient sodiumhydroxide was added to the bath molality. to raise the pH to 4.5. In thepreferred embodiment of the invention, TabZe B Relaxing Bath I TenacityElongation Ratios Denier Filament Ooagulant I pH IonMolality Dry WetLoop Dry Wet Loop W/D L/D gZ gQ 4.5 5.1 135 100 5.28 4. 42 2. 32 5.7 0.92.0 r 0. 84 0.44 Example v ggg g 4.9 2.8 140 100 4.83 3. 79 2.75 5.9 8.13.3 0.79 0.57 Example $35,5 5.0 1.7 156 100 s. 77 3.12 2.81 9.4 11.5 5.90.83 0.75

wet tenacity loop tenacity 1 WI D dry tenacity dry tenacity tions ofsodium sulfate as the relaxing bath, it is 3 to be understood that theinvention is not restricted to such bath. In general, an aqueoussolution of any water-soluble salt which will precipitate or coagulateviscosewithout substantial regeneration can be used. As illustrativeexamples of salts other than sodium sulfate which can be used areammonium sulfate, ammonium chloride, ammonium carbonate, sodiumphosphate, etc., or mixtures thereof, and with or without an alkali. Inthe claims, the expression an aqueous solution of a water-soluble saltwhich is a coagulant for cellulose xanthate is intended to define asolution containing such a salt or mixtures of such salts and with orwithout an alkali. I

It is assumed that the effect of the dilute salt baths on the swellingof the unregenerated gel yarns is primarily a function of the molalityof the ion present. However, since the hydroxyl ion exerts a specificswelling action on cellulose, the molality of the swelling bath must beincreased when above a pH of 7 to counterbalance the swelling action ofthehydroxyl ion. The molalityv of the solution is calculated as thenumber of gram ions per 1000. grams of solvent, assuming 100% ionizationbut disregarding the presence of hydrogen or hydroxyl ions.

Experiments have shown that for an aqueous relaxing solution of aneutral salt at an approximate pH of '7, the'preferable rangeof molalityis between 2'. and 3, with some definite beneficial effect between themolality of l and 4.. Below a molality of '1, excessive swelling andincipient solution occur, andabove a molalit of 4 little effect isobserved. Experiments have also shown that as the pH is increased above7, as, for example, by addition of alkali hydroxide, the molality of thesolution must be increased about 0.5 unit for every two unit change inpH so that at a pH of, for example, 11, the minimum useful range startsat a molality of 2 and the optimum range at a molality of 3. The upperlimits of the optimum range broadens considerably at higher pHs, so,that at a pH of 10 a molality of as high as 5 gives good effects. It isprobable that the upper the relaxing bath consists of an aqueoussolution of sodium sulfatehaving concentrations of from 9% to 13%.

The following aqueous solutions, containing the named coagulant andhaving the ion molality and pH values set forth in the following TableC, have also produced satisfactory results as relaxing solutions in themethod herein described:

Table C Ooagulant pH Ion Molality 7.0 1. 59 7. 0 2. 51 7. 0 3. 72 5. 0l. 59 5. 0 2. 51 5.0 3. 72 7. 0 l. 59 7. 0 2. 51 7.0 3. 72 10. 6 3.1410.0 5. 03 11. 25 2. 71 10.8 3.76 NEQSOl'iNflOH 9. 2 3.17

The means by which the unregenerated stretched yarn is subjected to therelaxing bath is not limited to those herein described. Ifdesired,immersion of trays of the relaxed unregeneratedyarn in the swelling bathcan be used. Also, the relaxing solution can be applied by both the dipbath of Figure 1 and the drip bath of Figure 2. The gel unregeneratedyarn at the time it is treated with the relaxing bath or while wet withthe relaxing solution is preferably in a substantially tension-freestate.

The duration of treatment with the relaxing bath is not critical and mayvary from 5 seconds to 1 hour or more.

The coagulating baths utilized in the above examples under theconditions present exert a strong and rapid coagulating effect onviscose without at the same time causing any substantial degree ofregeneration of the coagulated Xanthate structure. The pH of thecoagulating bath is maintained within the range of 3.0 to 7.0 andpreferably within the range of 3.5 to 5.5, and the coagulating bathcontains 10% or more of phosagsraees:

phosphate',-i."e., although all of the-phosphate allofthe'phosphateis'present as triso'diumphos phate. It is obvious that the phosphateradical may be'present inother forms, *forexample in the. form of mono-'or*disodiumphosphates; or

other' soluble phosphates, forexample the phos phates of alkali metalsother than sodium. EAlso, other phosphates such as" ammonium" phosphate,

organic amine phosphates and the like can be;

used- I-Iowever because. of the. greater efiiciency of the alkalimetallphosphates .in. the practice of theinventionlandtheir lesser.cost, alkali. metal.

phosphates-are preferred. 7

In describing the specific composition .of the. phosphate baths utilizedin the above examples, it

is to be understood that although the baths can bemade up fromcommercially" availableimaterials so as to have approximately thedesired. .pl-I, nevertheless it is usually advisable to add a: certainamount of phosphate, e. g. phosphoric acid or its salts, so as to adjustthe pH of the bath accurately to the desired value. Also, it is notnecessary for I the aqueouscomposition initially utilized inmaking up"the bath to possess a pH close to that desired since, by theaddition-of the proper amount of I Whatever phospha-te -is nee'de'd,the-desired pH can-be-attaine'd.

"The above examples utilize coagulating bathsv in which the phosphate ispresent largely; if not entirely, in the form ofmonosodium phosphate.The use of alkali metalphosphates is preferred, and the greater utilityof'the alkali metal phosphates is based,at least in part, on the factthat the monoand disodium phosphates existing as such under thepI-Iconditions prevailing in,the coagulating bath','and"being salt's'of astrong base and a weak acid- (the second-and third hydrogen atoms ofphosphoric acid'h'aving'a' low'degree of ionization), exhibit abuffering action in the bath, i. e. relatively'l'ar'ge amounts'ofthe'alkali' carried over in the viscosecanbeneutralized withoutmarkedly changing the pH of the bath. Other similar 'bufiering agentssuch as sodium acetate can,-if desired, be added'to supplement thebuffering action of the phosphate salts. This buffering characteristicmakes possible the rapid anduniformcoagulation-of the viscose due tothesubstantially constantconditions of the bath over relatively longperiodsof use. 1 By contrast, previously known coagulating bathsconsisting of aqueous solutions ofammonium sulfate (which havea pI-Iof-lessthan7l0) exhibit no 'buifering' action.

Although the coagulatingbath can comprise, if desired, an aqueoussolution containing only an alkali metal salt ofphosphoric aci'd in an'am'ount of 10% and preferabl3 l5% or'm'oreby-weight, in addition to thephosphate, the bathm'ay also containsalts of strong a'cid's. Thus-as-indi'ca-ted in Example I, the bath may also containsodium sulfate, onetypical-form of such bath being an aqueous solution --containing 20%monosoclium phosphate and from-2%to 20% of sodiumsulfate, the bath beingadjustedto a pH cf,'for example, 4.0150 4.5; Another material that canbe added to the phosphate bathswith advantage is-ammonium sulfate.

The coagulating bath is 'preferablymaintained at a temperature of45"to75" -C.,-the yarn-travel through the bath 1. preferably. beinguo'fth'e' order of' 2 in'ches to 1 8 inches. However, these temp'eraturesand bath travels: are not criticaLaprovide'd only'that they are not sogreat as to' cause. any-substantial degreeof'regeneration of-the 'cellulose'xa-nthate structures produced therein. The.

yarn must, however, be preferably completely coagulate-dbefore it issubjected to the subsequent stretching operation of the invention.'Wheri 10. the travel-throughthe-coagulating bathuis- "in-' sumcient -tocompletely coagulate the extruded viscose, it is desirable to lag theincompletely coag-ulated' yarn under low tension, for example-"by:passing it through air, for a time sufiicientto 15 complete thecoagulation. Or, if desired, the yarn can be passed through a secondphosphate coagulating bathv for .a period of time sufficient to completethe coagulation. If the yarn is not completely coagulated prior tostretching, the

amount of stretch obtainable will be distinctly impaired.

When the coagulating bath=isrendered unfit for further :use because ofthe" addition 1 of large amountsof caustic. from the viscosesolution,.it

can be reconditioned for further use by the ad- "dition offreshamountsofphosphoric acid. It can also be reconditioned by the a'dditionofis-ufiioient sulfuric acid to make the total sulfate ion content-::substantially :equivalent :to the -.total s'ddiumuionrcontent otithe'bath, the solution then being :concentratedbyr evaporation and stronglycooled to:0-" C..) tozcrystallize.out'sodium sulfate. The remainingconcentrated solution of phosphoricza'cid :can .then be .used. tostrengthen or re'conditionifurther volumes of waste bath.

F It. is important for coagulation to i take, place un'der 'conditionsof veryr'low tension. Thus, thetension imposed on; the filamentsinthecoagulatingbathishould notrbe. inexcesszoffll. gram 40 perdenier'iandpreferably not in excess=.of:.-020l. graimper denier.- :Wlhere theviscoseustructure: is nonefilamentary, tensions equivalent 1 to thosegiven J in connection with::filaments will be used.

The stretching zof athe 'coagulatedeonly yarn:

can be accomplished by passing the yarn about. positively :driven.pairs: offstretchingirollsrsor in any other :known manner. .Inaccordancew'ithi thievexamples, this stretching islpreferably pertormed 'while theyarn passing through a bath of'thesame general. type-as? thecoagulatingba-th, but heated. almost: to the boilfsince su'ch baths.assist in developing the-greatest degree, offstretch. However, this .is:not :essential. The: stretching operation can,if desi1ted,' be performedin. the.

1 presence of an aqueousrsolution of inorganic salts,

al-iquid such as glycer-in,itriethanolamine; ethylene glycol, etc., or.evenain. the presence. of 'a gaseous medium? such ras li-ve steam, air,:carbon dioxide, sulfur "dioxide, etc. These stretching media arepreferably maintained at an elevated.

temperature, for examp1e'.1'00 'C; or; more. Howevergthisis not."critical'itoezthe practicerof the invention and they can, ifsdesired,be maintained at .anyother temperature, .for example at roomtemperature. In accordancewithithe principles of this invention, theyarn at the start ofthe stretching operation issubstantially'Junregenerated and is water-soluble. The duration of thestretching operation and the contact of the yarn 7' with' the stretchingmedium-is preferably so short that no substantial amount of regenerationis effected.

The stretched relaxed 'yarn iscollected in suitable package form and"regenerated. "It-maybe 7'5 collected-oner0tating bobbinin-the formef across-wound package or in a centrifugal bucket of the type customarilyemployed in the spinning of viscose' rayon yarn, or it may be collectedin any other package form. Preferably, however, the yarn is permitted tofall in a relaxed, tens'ionless state on to a slowly moving support andformed into a cake-like package in the manner of Example I above. Theyarn package protected by a suitable cover is then treated with aregenerating bath for a suitable period of time. This bath can comprisea mineral acid solution, for example of the type generally employed inthe single bath process in the spinning of viscose rayon yarn andcontaining from 8% to sulfuric acid, together with varying amountsofinorganic salts such as sodium sulfate, etc., orit may comprise anaqueous inorganic salt solution or an inert liquid (such as glycerin)heated to a high temperature. Preferably, however, it comprises aboiling solutionof the same general type as the coagulating orstretching baths. -On the other hand, the yarn wet with occludedcoagulating bath and stretching bath liquors can be regeneratedbyspontaneous decomposition of the cellu lose xa'nthate by permitting itto stand a sumciently long time (for example 24 hours) at roomtemperature. In such a case, of course, the humidity of the surroundingatmosphere shouldbe maintained sufficiently high to preventcrystallization within'the yarn of those saltscontained in the occludedliquors.

It is not necessarythat the yarn be regenerated and purified in packageform. Thecoagulatedonly yarn can beled through a regenerating bath in acontinuous vmanner prior to its collection in package form, or the yarncan be collected in a tensionless manner on a slowly moving conveyorbelt of the type shown in British Patent No. 379,880 toTopham, the yarncollected in the form of small overlapping ringlets being subsequentlyled under showers of regeneratingand purifying liquids and dried.Although any method can be used in preparing the viscose utilized in thepractice of the invention, the viscose employed in the examples wasprepared by a standardmethocl involving the combination of alkali (soda)cellulose with the percentage of carbon bisulfide (recited in theexamples) based on the cellulose content of the alkali cellulose. Also,vlscoses having a wide range of viscosities may be. used, but itispreferred that viscoses which have been submitted to a very shortripening period and have a salt index of about 2.0to 2.5 be spun. Theuse of the strong coagulating baths of this invention causes rapidcoagulation of such viscoses'. It is also preferred, although notcritical, that the alkali celluloseused be subjected only to a shortaging period.

It is preferred, in order to develop the greatest stretchability of thecoagulated, unregenerated structures, to utilize viscose in which thecaustic content is higher than the cellulose content, e. g. a viscosecontaining 7% cellulose and 9% sodium hydroxide. However, other viscoseswhich have a sodium hydroxide content less than the cellulose may alsobe used and, generally speaking, viscoses having a cellulose or causticcontent of between 4% and 9%, or more, are quite satisfactory.

The invention can be applied to continuous spinning, purification andcollection processes of any character.

In carrying out the invention, it is possible to produce 1 eitherstraight or 1 'crimped.. filaments.

For examplawherethe coagulating baths contain, in addition tophosphates, a high concentration, e. g. 20%, ofammonium sulfate 'or ofsodium sulfate, or both, then filaments are produced which have a goodpermanent crimp or which develop a good permanent crimp when treated ina state free of substantial tension with water or dilute aqueous causticsoda. If the stretched yarn is regenerated in a state free ofsubstantial tension, even though tension is applied during thesubsequent'steps of washing and drying, the yarn develops a decideddegree of crimp upon treatment with hot water or dilute caustic 'soda'.Also,- even though tension is used during regeneration and subsequentpurification and drying treatments and thereby acquires no crimp,nevertheless, it will develop a very good permanent crimp upon beingtreated in a relaxed state in hot water or dilute caustic solution.

As is shown by the above tables, the transverse properties of the rayontreated in accordance with this invention are materially improved. Thisis indicated by the improved loop tenacity without marked loss in drytenacity.

As is shown by the tables, yarn prepared by the preferred sodium sulfaterelaxation have generally improved loop strengths (up to 0.5 to 0.6 gramper denier greater than the controls), decreased wet and dry tenacities(losses of approximately 0.5 gram denier in each), and greater wet, dryand loop elongations than rayon spun by identical processes but omittingthe relaxation treatment.

The relaxed yarns are considerably less brittle than yarns prepared byidentical processes except that the relaxing treatment is omitted. "As ageneral rule the yarns of this invention are duller in appearance andappear to show a tendency toward waviness. The improved properties ofthe yarn of this invention become apparent from the following table:

Table D Number 01' Den1/Fil. Flexes to Failure 1 Yarn with relaxingtreatment of this invention 1. 42 l, 450 Yarn. Without relaxingtreatment of this invention v1.35, 450

, Determined on Masland flex tester.

The invention not only makes it possible to produce a yarn of verydesirable properties, but also makes possible a spinning process that isadmirably adapted for use on a commercial scale. The process does notrequire the use of complicated apparatus or difi'icultly prepared baths.

The invention has its principal utility in the manufacture of filamentsand yarns. However, the invention, broadly speaking, is applicable alsoto the production of thin tubing and other types of products by theviscose process with the attaining of genenally the same advantageswhich result from the use of the invention in the manufacture offilaments and yarns.

Since the operation of the invention as described above is capable ofconsiderable modification, any variation which conforms to the spirit ofthe invention is intended to be included within the claims.

I claim: q I

1. In the process for the production oi' a'regenerated cellulosestructure which comprises extruding v-isboseiintoa coagulating bathwhich will precipitate the cellulose xanthate without substantiallyconverting 'it a to regenerated cellulose, drawing said structure fromsaid batlystretching said structure "and regenerating the-same toregeneratedcellulose; the improvement'which comprises thestep-l-of'swelling the structure "subsequent to=stretchingin-thepresence of; an aqueous solutionzof a. water-soluble salt which is acoagulant i'or' cellulosexanthate, said solution having ancion'molality*withinthe limits defined by the generated cellulose; the-improvementwhich comprises the step of-swelling 'the structuresubsequenttostretching and; prior to regeneration in the'presence'ofwanaqueous solution of a watersolulolje salt which is acoagulant forcellulose xanthate, said solution having an ion mol'ality withinthe-limits definedby the curves -AB and GDof'the graph shcwn-as Figur 4in the accompanying-drawings and'the pH at the point on the ordinateof-sa-id graph correspondingto said ion molality. a

"3. 111 the process for the production'of ':a regenerated-cellulosestructure which comprises extrudingviscose into a coagulating bath whichwill precipitate the cellulose-xanthate without substantiallyconver-tingit "to regenerated cellulose, drawing said structure from said bath,stretching said structure and regenerating the same to regeneratedcellulose, the improvement which com prises th step of swelling thestructure subsequent to stretching and simultaneously with regenerationin the presence of an aqueous solution of a water-soluble salt which isa coagulant for cellulose xanthate, said solution having an ion molalitywithin the limits defined by the curves AB and CD of the graph shown asFigure 4 in the accompanying drawings and the pH at the point on thordinate of said graph corresponding to said ion ln'olality.

4. In the process for the production of a regenerated cellulosestructure which comprises extruding viscose into'a coagulating bathwhich will .precipitatethe cellulose Xanthate Without sub: stantiallyconverting-it to regenerated cellulose, drawing said structure from saidbath, stretching said structure and regenerating the-same to regeneratedcellulose, the improvement which comprises the step of swelling thestructure subsequent to stretching in the presence of an aqueoussolution of a water-soluble salt which is a coagulant for cellulosexanthate, said solution havinganion molality within the limits definedby the curves EF and GH of the graph shown as Figure 4 in theaccompanying drawings and the pH at the point on the ordinate ofsaid-graph corresponding to said ion molality.

5. In the process for the production of a regenerated cellulosestructure which comprises extruding viscose into a coagulating bathwhich will precipitate the cellulose xanthate without substantiallyconverting it to regenerated cellulose, drawing said structure from said'bath, stretching *sa d'; structure and. regenerating the ome-to. eeenra d ce u ose, the: improv ment ich -'comp e h -st p'iof wellingzt e trt ture subsequent to stretching and prior to regeneration in thepresence of anaqueous solution ofa water-soluble salt which is acoagulant for cellulose xanthate, said, solution having an ion molalitywithin the limits defined by the curves EFandGI-I of the graph shownaS-Eigure 4 in theaccompanying drawings and the-pH at the. point on theordinate of -said. graph correspond! ing to said ion molality.

v .6. In the process ior. the production of-a regenerated cellulose.structure whichcQm-ptiSes ex-e trud-ing viscose into a coagulatingbathwhich will prec-ipitate the cellulose xanthate without,substantially converting it to regenerated ten lulose, diawing saidstructure from said bath, s etching aid struc ure and r nera ng hsameeto regenerated cellulose, the im rovement. which comprises the stepof swelling the structure subsequent to stretching and simultaneouslywith regeneration inlthe presence of. an aqueous, solution of awater-soluble salt which is aflcoagu lant for cellulosexanthate,saidsolutionhaviris/11.1v ion. molality. within he limits defined by thecurves 'EF and GH of the graph Shown s Figur 4 nt accompany ng draw ngsrid. the pH a he point'o.n the ordinate of said. raph cor spond ngtosaidio molality- ,111. the nr ess'for t e pr ducti n of a regeneratedcellulose structure win 11' comprises exruding vi os into a coa ulating"bath whi ill precipitate the cellulos xanthate withou sub a ly nvertinFit to r gen ra ed cellulose, drawin said st u tu e from sa a h! stret hn aidls u tur a d e e ra ng t e sa e. t e enera ed c l l se, the improvee t whichcomprises the step of swelling the st'rhctjujre 1 subsequent tostretching in theflpre'selitie of an aqueous solution, of afwate rsoluble neutral salt which is a, coagulant for lcellulose'fxanthate,said solution having an ion-molality of from 11104 an a fl r a- 8. Intheprocess for the procluotio'n ofia' regenerated cellulose structurewhich comprises extruding viscose into a coagulating hath-which willprecipitate the cellulose ,Xanthate without substantially converting itto regenerated cellulose, f drawing "said structure from said bath,stretching said structure and regeneratingfthe same to regeneratedcellulose,- the improvement which comprises thestep 'of swelling'tliestructure subsequent to stretching in the presence' of an aqueoussolution'offa 'water-solubleneutral salt which is acoagulantior'cellulose 'xanth'ate, said solutionhaving an ion'rnol'alit'yof frame to 3 afid'a pH of 'l. v

'9. In the process for the production "ofai-egenerated cellulosestructurewhich comprises extruding viscose into a coagulating bath-whichwill precipitate the cellulose Xanthate "withoutsubstantially"convertingit to regenerated"cellulose, drawing saidstructure "from said "bath, stretching saidstructure "and regeneratingthe samet'o regenerated cellulose, the'iniprovement which comprises thestep" of' swellingthestructure 'subseq'uent to stretching in'the'presence of an aqueous solution having a pH ofi'l'iand 1 an ion'molality of froml to '4 and consisting ofwater and sodium sulfate, thelatter being present in an amount of from 9% to 13% by weight 'of' thesolution. I 7

10.'In the process for'the production ofi-airegenerated cellulose yarnwhich comprisesextruding viscose filaments into a coagulating bath which@willwprecipitate :-the cellulose xanthate ment which comprises the stepof swelling the filaments subsequent to stretching in the presence of anaqueous solution ofa water-soluble salt which is a coagulant forcellulose xanthate, said solution having an ion'rmolality within thelimits defined by the curves AB and CD of the graph shown as Figure 4 inthe accompanying drawings and the pH at the point, on the ordimate ofsaid graph corresponding to said ion molality.

11. In the process for theproduction of a regenerated cellulose yarnwhich comp-rises extruding viscose filaments into a coagulating bathwhich will precipitate the cellulose xanthatc without substantiallyconverting it to regenerated cellulose, drawing said filaments from saidbath, stretching said filaments and regenerating said filaments toregenerated cellulose, the improvement which comprises the step ofswelling the filaments subsequent to stretching and prior toregeneration in the presence of an aqueous solululose, drawing saidfilaments from said bath,

stretching said filaments and regenerating said filaments to regeneratedcellulose, the improvement which comprises the step of swelling thefilaments subsequent to stretching and simultaneously with regenerationin the presence of an aqueous solution of a water-soluble salt which isa coagulant for cellulose xanthate, said solution having an ion molalitywithin the limits defined by the curves AB and CD of the graph shown asFigure 4 in the accompanying drawings and the pH at the point on theordinate of said graph corresponding to said ion molality.

13. In the process for the production of a regenerated cellulose yarnwhich comprises extruding viscose filaments into a coagulating bathwhich will precipitate the cellulose xanthate without substantiallyconverting it to regenerated cellulose, drawing said filaments from saidbath, stretching said filaments and regenerating said filaments toregenerated cellulose, the improvement which comprises the step ofswelling the filaments subsequent to stretching in the presence of anaqueous solution of a water-soluble salt which is a coagulant forcellulose xanthate, said solution having an ion molality within thelimits defined by the curves EF and GH of the graph shown as Figure 4 inthe accompanying drawings and the pH at the point on the ordinate ofsaid graph corresponding to said ion molality.

14. In the process for the production of a regenerated cellulose yarnwhich comprises extruding viscose filaments into a coagulating bathwhich will precipitate the cellulose xanthate without substantiallyconverting it to regenerated cellulose, drawing said filaments from saidbath, stretching said filaments and regenerating said filaments toregenerated cellulose, the improve- 18 ment :-which comprisesthe step ofswelling the filaments subsequent to stretching and prior toregeneration in the presence of an aqueous solution of awater-solublesalt which is a coagulant for cellulose xanthate, saidsolution having. an ion molality within the limits defined by the curvesEF and GI-Iof the graph shown as Figure 4 intheaccompanying drawings andthe'pH at the point on ithe iordinate of said graph corresponding tosaid ion molality.

15. In the process for the production of a regenerated cellulose yarnwhich comprises extruding viscose filaments into a coagulatin bath whichwill precipitate the cellulose xanthate without substantially convertingit to regenerated cellulose, drawing said filaments from said bath,-stretching said filaments and regenerating said filaments to regeneratedcellulose, the improve ment which comprises the step of swelling thefilaments subsequent to stretching and simul-'-' taneously withregeneration in the presence of an aqueous solution of a water-solublesalt which is a, coagulant for cellulose xanthate, said solution havingan ion molality within the limits defined by the curves EF and GH of thegraph shown as Figure 4 in the accompanying drawings and the pH at thepoint on the ordinate of said graph corresponding to said ion molality.

16. In the process for the production of a regenerated cellulose yarnwhich comprises extruding viscose filaments into a coagulating bathwhich will precipitate the cellulose Xanthate without substantiallyconverting it to regenerated cellulose, drawing said filaments from saidbath,

stretching said filaments and regenerating said filaments to regeneratedcellulose, the improvement which comprises the step of swelling thefilaments subsequent to stretching in the presence of an aqueoussolution of a water-soluble neutral salt which is a coagulant forcellulose xanthate, said solution having an ion molality of1to4andapI-Iof7.

17. In the process for the production of a regenerated cellulose yarnwhich comprises extruding viscose filaments into a coagulating bathwhich will precipitate the cellulose xanthate without substantiallyconverting it to regenerated cellulose, drawing said filaments from saidbath, stretching said filaments and regenerating said filaments toregenerated cellulose, the improvement which comprises the step ofswelling the filaments subsequent to stretching in the presence of anaqueous solution of a water-soluble neutral salt which is a coagulantfor cellulose xanthate, said solution having an ion molality of2to3andapI-Iof'7.

18. In the process for the production of a regenerated cellulose yarnwhich comprises extruding viscose filaments into a coagulating bathwhich will precipitate the cellulose xanthate without substantiallyconverting it to regenerated cellulose, drawing said filaments from saidbath, stretching said filaments and regenerating said filaments toregenerated cellulose, the improvement which comprises the step ofswelling the filaments subsequent to stretching in the presence of anaqueous solution having a pH of '7 and an ion molality of from 1 to 4and consisting of water and sodium sulfate, the latter being present inan amount of from 9% to 13% by weight of the solution.

19. In the process defined in claim 1 wherein the aqueous swellingsolution contains a mixture of Water-soluble salts.

20. In the process defined in claim 5 wherein "the aqueous swellingsolution contains :a mix- 'ture of water-soluble salts.

-21. In the processdefined in claiml wherein the aqueous swellingsolution contains an alkali hydroxide when said solution has a 'pI-Iabove 7. 5

22. In the process defined in claim 5 wherein 'the aqueous swellingsolution contains an alkali hydroxide when said solution has a pH above7.

LINTON G. RAY, JR.

REFERENCES YCITED The following references are of re'c'ort'i'in the 1"file of this patent: v

UNITED STATES PATENTS

1. IN THE PROCESS FOR THE PRODUCTION OF A REGENERATED CELLULOSESTRUCTURE WHICH COMPRISES EXTRUDING VISCOSE INTO A COAGULATING BATHWHICH WILL PRECIPITATE THE CELLULOSE XANTHATE WITHOUT SUBSTANTIALLYCONVERTING IT TO REGENERATED CELLULOSE, DRAWING SAID STRUCTURE FROM SAIDBATH, STRETCHING SAID STRUCTURE AND REGENERATING THE SAME TO REGENERATEDCELULOSE, THE IMPROVEMENT WHICH COMPRISES THE STEP OF SWELLING THESTRUCTURE SUBSEQUENT TO STRETCHING IN THE PRESENCE OF AN AQUEOUSSOLUTION OF A WATER-SOLUBLE SALT WHICH IS A COAGU-